How many devices in a Broadcase Domain before Segmenting?

Discussion in 'Cisco' started by Joel M. Baldwin, Nov 4, 2004.

  1. How many Ethernet devices can be on a Broadcast Domain before performance
    starts to suffer?

    I'm sure it's been asked here before, but I haven't been able to find
    a good answer. >IS< there a single good answer, or is it "It depends!"

    We have a fully switched network with around 250 devices spread across
    two C addresses that are attached across 19 2948 and 3548 switches.
    These 19 switches in turn are connected via 1 gig ether to a single
    3750 switch. Everything at the moment is strictly L2 on a single VLAN
    with the only routing in the 3750 being between subnets.

    However we're about to increase the number of devices up to between 500
    and 600 devices. I'm starting to think that I need to segment the network
    into 4 VLANs and turn on L3 routing.

    Am I crazy to think this? I don't want to wait until after problems
    start, but likewise don't want to do unnecessary work.

    ADVthaAnksNCE
     
    Joel M. Baldwin, Nov 4, 2004
    #1
    1. Advertising

  2. Joel M. Baldwin

    Ben Guest

    It does depend on what protocols you are running. IPX used to be a problem
    as there was so much broadcast traffic, nowadays not so much. 500+ hosts
    would be a fairly large broadcast domain. You can always look at your
    interface stats to get an idea of the amount of broadcast traffic. But
    consider every time a host ARPs to find another ip on the same subnet
    everyone is going to have to process the frame...

    "Joel M. Baldwin" <> wrote in message
    news:Xns9597DDCE6E48qumqatscalwebcom@66.250.146.150...
    >
    > How many Ethernet devices can be on a Broadcast Domain before performance
    > starts to suffer?
    >
    > I'm sure it's been asked here before, but I haven't been able to find
    > a good answer. >IS< there a single good answer, or is it "It depends!"
    >
    > We have a fully switched network with around 250 devices spread across
    > two C addresses that are attached across 19 2948 and 3548 switches.
    > These 19 switches in turn are connected via 1 gig ether to a single
    > 3750 switch. Everything at the moment is strictly L2 on a single VLAN
    > with the only routing in the 3750 being between subnets.
    >
    > However we're about to increase the number of devices up to between 500
    > and 600 devices. I'm starting to think that I need to segment the network
    > into 4 VLANs and turn on L3 routing.
    >
    > Am I crazy to think this? I don't want to wait until after problems
    > start, but likewise don't want to do unnecessary work.
    >
    > ADVthaAnksNCE
     
    Ben, Nov 4, 2004
    #2
    1. Advertising

  3. Joel M. Baldwin

    stephen Guest

    "Ben" <> wrote in message
    news:AHsid.11987$...
    > It does depend on what protocols you are running. IPX used to be a problem
    > as there was so much broadcast traffic, nowadays not so much. 500+ hosts
    > would be a fairly large broadcast domain. You can always look at your
    > interface stats to get an idea of the amount of broadcast traffic. But
    > consider every time a host ARPs to find another ip on the same subnet
    > everyone is going to have to process the frame...
    >
    > "Joel M. Baldwin" <> wrote in message
    > news:Xns9597DDCE6E48qumqatscalwebcom@66.250.146.150...
    > >
    > > How many Ethernet devices can be on a Broadcast Domain before

    performance
    > > starts to suffer?
    > >
    > > I'm sure it's been asked here before, but I haven't been able to find
    > > a good answer. >IS< there a single good answer, or is it "It depends!"


    It depends....
    > >
    > > We have a fully switched network with around 250 devices spread across
    > > two C addresses that are attached across 19 2948 and 3548 switches.
    > > These 19 switches in turn are connected via 1 gig ether to a single
    > > 3750 switch. Everything at the moment is strictly L2 on a single VLAN
    > > with the only routing in the 3750 being between subnets.
    > >
    > > However we're about to increase the number of devices up to between 500
    > > and 600 devices. I'm starting to think that I need to segment the

    network
    > > into 4 VLANs and turn on L3 routing.


    there are lots of reasons for routing - you already have 1 with 2 subnets.

    once you start to route, then split the layer 2 subnets up - that way you
    get a few advantages:

    easier to fault find.
    lower background traffic (broadcasts)
    central switch becomes the place to monitor and interconnect devices.
    you dont have to handle the wierd effects of secondary IP addresses on the
    central switch.
    you can have resilience without needing spanning tree to stabilise loops.

    If your servers are connected at the centre, then that becomes the "star"
    point for traffic.

    Putting the servers on that central switch in their own subnet / VLAN helps
    if you ever have to filter IP, and you can put a 2nd switch in parallel if
    you decide you need some resilience.
    > >
    > > Am I crazy to think this? I don't want to wait until after problems
    > > start, but likewise don't want to do unnecessary work.



    > >
    > > ADVthaAnksNCE

    --
    Regards

    Stephen Hope - return address needs fewer xxs
     
    stephen, Nov 4, 2004
    #3
    1. Advertising

Want to reply to this thread or ask your own question?

It takes just 2 minutes to sign up (and it's free!). Just click the sign up button to choose a username and then you can ask your own questions on the forum.
Similar Threads
  1. Henry Yen

    Segmenting 2900xl?

    Henry Yen, Jun 15, 2004, in forum: Cisco
    Replies:
    0
    Views:
    463
    Henry Yen
    Jun 15, 2004
  2. Henry Yen

    segmenting/splitting 2900XL?

    Henry Yen, Jun 15, 2004, in forum: Cisco
    Replies:
    4
    Views:
    592
    Henry Yen
    Jun 20, 2004
  3. Mark Scott

    segmenting a fibre backbone network

    Mark Scott, Feb 16, 2005, in forum: Cisco
    Replies:
    3
    Views:
    709
  4. Replies:
    12
    Views:
    1,554
  5. Limited Wisdom
    Replies:
    7
    Views:
    799
    Jonathan Roberts
    Sep 13, 2006
Loading...

Share This Page